In general, organic molybdenum compounds are known to improve the lubricating properties of engine oils. For example, molybdenum dithiocarbamates are typically employed for the reduction of friction. The molybdenum dithiocarbamates, however, contain sulfur and slowly lose the ability to reduce friction unless an alternate sulfur source is present in the lubricating oil. Another example of organic molybdenum compounds are sulfurized molybdenum polyisobutenyl succinimide complexes which are used to mediate wear, reduce friction, and/or control oxidation. See, e.g., U.S. Pat. Nos. 4,259,194; 4,265,773; 4,283,295; 4,285,822; and 6,962,896 and U.S. Patent Application Publication No. 2005/0209111. Problems associated with the use of sulfur in lubricating oils are that sulfur can be incompatible with emission control devices and can result in corrosion problems.
U.S. Pat. Nos. 4,357,149 and 4,500,439 disclose molybdated C15-C20 alkenyl succinimides. In Example XI of both of these patents, a molybdated succinimide is prepared by reacting a C15-C20 alkenyl succinic anhydride with triethylene tetramine followed by treatment with a molybdic acid solution.
Russian Patent No. 2201433 discloses a molybdated succinimide post-treated with maleic anhydride as an additive for motor oils used in internal combustion engines. Russian Patent No. 2201433 further discloses that the additives are prepared by reacting an alkenyl succinimide of polyethylene polyamine with anunonium molybdate in the presence of water as a promoter and then reacting the resulting product with maleic anhydride taken in amounts of 0.2 to 1.0 mole per 1 mole of alkenyl succinimide of polyethylene polyamine. All of the examples disclosed in Russian Patent. No. 2201433 employ a high molecular weight polyisobutenyl (950 M.W.) succinic anhydride (PIBSA) in preparing the alkenyl succinimide of polyethylene polyamine.
Molybdenum succinimide complexes are also described in U.S. Patent Application Publication No. 2009/0325832. These complexes are prepared by a process comprising (a) reacting an alkyl or alkenyl succinimide of a polyamine, with an ethylenically unsaturated carboxylic acid or anhydride thereof; and (b) reacting the product of step (a) with an acidic molybdenum compound. Also disclosed is a lubricating oil composition containing at least (a) a major amount of a base oil of lubricating viscosity and (b) a minor amount of the molybdated succinimide complex.
It is desirable in certain applications (e.g. wear inhibition, oxidation control, and friction performance) for additives to contain a high concentration of molybdenum and basic nitrogen, in addition to other physical and handling properties such as being lower in color intensity. Also desirable is a process which does not result in particulate matter in the final product.